Communication control method, user terminal, processor, storage medium, and base station

ABSTRACT

A communication control method applied to a mobile communication system including a user terminal capable of storing an MDT measurement log related to a radio environment measured based on an instruction from a network and a connection establishment failure log related to a failure of RRC connection establishment procedure with the network, the method includes the steps of: reserving a dedicated memory area for storing the connection establishment failure log, by the user terminal; and storing the connection establishment failure log in the dedicated memory area reserved in the reserving step, by the user terminal.

TECHNICAL FIELD

The present invention relates to a communication control method appliedto a mobile communication system, a user terminal, a processor, astorage medium, and a base station.

BACKGROUND ART

In a mobile communication system, if a building is built in the vicinityof a base station, or if the installation status of a base station inthe vicinity of the base station changes, the radio environment relatedto the base station changes. Therefore, conventionally, drive tests tomeasure and collect the radio environment are carried out by an operatorwith using a measurement vehicle on which a measuring instrument isinstalled.

Such measurement and collection may contribute to network optimization(for example, coverage optimization due to adjustment of parameters ofthe base station). However, there are problems in that the number ofprocesses and cost increase.

Thus, in 3GPP (3rd Generation Partnership Project), which is a projectaiming to standardize a mobile communication system, MDT (Minimizationof Drive Tests) for automation of the measurement and collection usinguser terminals has been specified on and after Release 10 (seeNon-patent Document 1, for example).

An example of the MDT is Logged MDT. In the Logged MDT, the userterminal in an idle state stores MDT measurement logs related to radioenvironments measured based on an instruction from a network and thentransmits (reports) the stored MDT measurement logs to the networklater.

PRIOR ART DOCUMENT Non-Patent Document

-   Non-patent Document 1: 3GPP technology specifications TS 37.320    V10.4.0 December, 2011

SUMMARY OF THE INVENTION

However, the user terminal may fail to access to the network. The access(RRC connection establishment procedure) includes a random accessprocess onto the network and a connection establishment process forperforming establishment (including re-establishment) of connection withthe network after the random access process.

Information about the access failure is useful for the networkoptimization described above. Disadvantageously, in the currentspecification, since there is no method for appropriately treating theinformation about the access failure, there is a problem in that thenetwork is not sufficiently optimized.

Accordingly, an object of the present invention is to provide acommunication control method, a user terminal, a processor, a storagemedium, and a base station with which it is possible to appropriatelytreat information related to access failure to a network.

To solve the above problems, the present invention includes thefollowing characteristics.

A communication control method according to a first feature is appliedto a mobile communication system including a user terminal capable ofstoring an MDT measurement log related to a radio environment measuredbased on an instruction from a network and a connection establishmentfailure log related to a failure of RRC connection establishmentprocedure with the network. The method includes the steps of: reservinga dedicated memory area for storing the connection establishment failurelog, by the user terminal; and storing the connection establishmentfailure log in the dedicated memory area reserved in the reserving step,by the user terminal.

A communication control method according to a second feature is appliedto a mobile communication system including a user terminal capable ofstoring a connection establishment failure log related to a failure ofRRC connection establishment procedure with a network. The methodincludes the steps of: when starting the RRC connection establishmentprocedure, starting a timer defining an upper limit time to continue theRRC connection establishment procedure, by the user terminal; andstoring the connection establishment failure login association with anexpiry of the timer, by the user terminal.

A communication control method according to a third feature is appliedto a mobile communication system including a user terminal capable ofstoring an MDT measurement log related to a radio environment measuredbased on an instruction from a network and a connection establishmentfailure log related to a failure of RRC connection establishmentprocedure with the network. The method includes: a step of transmittingnotification information indicating that a log is stored, from the userterminal to the network, by a predetermined trigger, when at least oneof the MDT measurement log and the connection establishment failure logis stored. The notification information is configured to be capable ofidentifying a type of the log stored by the user terminal.

A communication control method according to a fourth feature is appliedto a mobile communication system including a user terminal capable ofstoring a connection establishment failure log related to a failure ofRRC connection establishment procedure with a network. The methodincludes: a step of transmitting, from the user terminal to the network,the connection establishment failure log and elapsed time informationindicating an elapsed time from an occurrence time point of the failureof RRC connection establishment procedure.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a configuration diagram of a mobile communication systemaccording to an embodiment.

FIG. 2 is a block diagram of UE according to the embodiment.

FIG. 3 is a block diagram of eNB according to the embodiment.

FIG. 4 is a protocol stack diagram of a radio interface according to theembodiment.

FIG. 5 is a configuration diagram of a radio frame used in the mobilecommunication system according to the embodiment.

FIG. 6 is a sequence diagram of an access procedure according to theembodiment.

FIG. 7 is a diagram for describing a method 1 of managing a memory areaaccording to the embodiment.

FIG. 8 is a diagram for describing a method 2 of managing a memory areaaccording to the embodiment.

FIG. 9 is a diagram for describing time information according to theembodiment.

FIG. 10 is a sequence diagram of a method 1 of reporting a log accordingto the embodiment.

FIG. 11 is a sequence diagram of a method 2 of reporting a log accordingto the embodiment.

FIG. 12 is a sequence diagram of a method 3 of reporting a log accordingto the embodiment.

FIG. 13 is a diagram for describing a method of reporting a logaccording to another embodiment.

FIG. 14 is a diagram for describing an example of time stamp without theneed for absolute time.

FIG. 15 is a diagram for describing an example of Timer expired case.

DESCRIPTION OF EMBODIMENTS

A communication control method according to embodiments is applied to amobile communication system including a user terminal capable of storingan MDT measurement log related to a radio environment measured based onan instruction from a network and a connection establishment failure logrelated to a failure of RRC connection establishment procedure with thenetwork. The method includes the steps of: reserving a dedicated memoryarea for storing the connection establishment failure log, by the userterminal; and storing the connection establishment failure log in thededicated memory area reserved in the reserving step, by the userterminal.

According to the embodiments, in the reserving step, the user terminalreserves the dedicated memory area separately from a predeterminedmemory area for storing the MDT measurement log.

A user terminal according to embodiments is capable of storing an MDTmeasurement log related to a radio environment measured based on aninstruction from a network and a connection establishment failure logrelated to a failure of RRC connection establishment procedure with thenetwork. The user terminal reserves a dedicated memory area for storingthe connection establishment failure log and then stores the connectionestablishment failure log in the dedicated memory area.

A processor according to embodiments executes a process for storing, ina memory, an MDT measurement log related to a radio environment measuredbased on an instruction from a network and a connection establishmentfailure log related to a failure of RRC connection establishmentprocedure with the network, the processor provided in a user terminal.The processor reserves a dedicated memory area for storing theconnection establishment failure log and then stores the connectionestablishment failure log in the dedicated memory area.

A storage medium according to embodiments stores a program that causes auser terminal capable of storing an MDT measurement log related to aradio environment measured based on an instruction from a network and aconnection establishment failure log related to a failure of RRCconnection establishment procedure with the network, to execute: a stepof reserving a dedicated memory area for storing the connectionestablishment failure log; and a step of storing the connectionestablishment failure log in the dedicated memory area reserved in thereserving step.

A communication control method according to embodiments is applied to amobile communication system including a user terminal capable of storinga connection establishment failure log related to a failure of RRCconnection establishment procedure with a network. The method includesthe steps of: when starting the RRC connection establishment procedure,starting a timer defining an upper limit time to continue the RRCconnection establishment procedure, by the user terminal; and storingthe connection establishment failure login association with an expiry ofthe timer, by the user terminal.

According to the embodiments, the RRC connection establishment procedureincludes a random access process onto the network. In the storing step,the user terminal stores a number of transmissions of random accesspreambles in the random access process, in the connection establishmentfailure log.

According to the embodiments, in the storing step, when the userterminal detects a contention of random access preambles, the userterminal stores information indicating a detection of the contention, inthe connection establishment failure log.

A user terminal according to embodiments is capable of storing aconnection establishment failure log related to a failure of RRCconnection establishment procedure with a network. The user terminalincludes: a controller that starts a timer defining an upper limit timeto continue the RRC connection establishment procedure when starting theRRC connection establishment procedure. The controller stores theconnection establishment failure log in association with an expiry ofthe timer.

A processor according to embodiments executes a process to store aconnection establishment failure log related to a failure of RRCconnection establishment procedure with a network, the processorprovided in a user terminal. The processor executes: a process ofstarting a timer defining an upper limit time to continue the RRCconnection establishment procedure when starting the RRC connectionestablishment procedure; and a process of storing the connectionestablishment failure login association with an expiry of the timer.

A storage medium according to embodiments stores a program that causes auser terminal capable of storing a connection establishment failure logrelated to a failure of RRC connection establishment procedure with anetwork, to execute: a process of starting a timer defining an upperlimit time to continue the RRC connection establishment procedure whenstarting the RRC connection establishment procedure; and a process ofstoring the connection establishment failure log in association with anexpiry of the timer.

A communication control method according to embodiments is applied to amobile communication system including a user terminal capable of storingan MDT measurement log related to a radio environment measured based onan instruction from a network and a connection establishment failure logrelated to a failure of RRC connection establishment procedure with thenetwork. The method includes: a step of transmitting notificationinformation indicating that a log is stored, from the user terminal tothe network, by a predetermined trigger, when at least one of the MDTmeasurement log and the connection establishment failure log is stored.The notification information is configured to be capable of identifyinga type of the log stored by the user terminal.

According to the embodiments, when the user terminal stores theconnection establishment failure log, the notification informationindicates that the user terminal stores the connection establishmentfailure log.

According to the embodiments, the method further includes: a step oftransmitting, from the network to the user terminal, request informationfor requesting a transmission of the log, based on the notificationinformation after receiving the notification information from the userterminal. The request information is configured to be capable ofidentifying a type of the log for which the transmission is requested bythe network.

According to the embodiments, the predetermined trigger is an event thatthe user terminal establishes or re-establishes a connection with thenetwork.

A user terminal according to embodiments is capable of storing an MDTmeasurement log related to a radio environment measured based on aninstruction from a network and a connection establishment failure logrelated to a failure of RRC connection establishment procedure with thenetwork. The user terminal transmits notification information indicatingthat a log is stored, to the network, by a predetermined trigger, whenat least one of the MDT measurement log and the connection establishmentfailure log is stored. The notification information is configured to becapable of identifying a type of the log stored by the user terminal.

A processor according to embodiments is provided in a user terminal. Theprocessor executes: a process of storing, in a memory, an MDTmeasurement log related to a radio environment measured based on aninstruction from a network and a connection establishment failure logrelated to a failure of RRC connection establishment procedure with thenetwork; and a process of transmitting notification informationindicating that a log is stored, to the network, by a predeterminedtrigger, when at least one of the MDT measurement log and the connectionestablishment failure log is stored. The notification information isconfigured to be capable of identifying a type of the log stored by thememory.

A storage medium according to embodiments stores a program that causes auser terminal capable of storing an MDT measurement log related to aradio environment measured based on an instruction from a network and aconnection establishment failure log related to a failure of RRCconnection establishment procedure with the network, to execute: a stepof transmitting notification information indicating that a log isstored, to the network, by a predetermined trigger, when at least one ofthe MDT measurement log and the connection establishment failure log isstored. The notification information is configured to be capable ofidentifying a type of the log stored by the user terminal.

A base station according to embodiments establishes a connection with auser terminal capable of storing an MDT measurement log related to aradio environment measured based on an instruction from a network and aconnection establishment failure log related to a failure of RRCconnection establishment procedure with the network. The base stationtransmits, to the user terminal, request information for requesting atransmission of a log, based on notification information after receivingthe notification information from the user terminal. The requestinformation is configured to be capable of identifying a type of the logfor which the transmission is requested by the base station.

A communication control method according to embodiments is applied to amobile communication system including a user terminal capable of storinga connection establishment failure log related to a failure of RRCconnection establishment procedure with a network. The method includes:a step of transmitting, from the user terminal to the network, theconnection establishment failure log and elapsed time informationindicating an elapsed time from an occurrence time point of the failureof RRC connection establishment procedure.

According to the embodiments, the method further includes: a step ofstarting a timer when the failure of RRC connection establishmentprocedure occurs, by the user terminal. In the transmitting step, theuser terminal transmits information indicating a value of the timer at atime point of transmitting the connection establishment failure log, asthe elapsed time information.

According to the embodiments, the method further includes: a step ofretaining the connection establishment failure log without deletinguntil the value of the timer exceeds a threshold value after startingthe timer, by the user terminal.

A user terminal according to embodiments is capable of storing aconnection establishment failure log related to a failure of RRCconnection establishment procedure with a network. The user terminaltransmits, to the network, the connection establishment failure log andelapsed time information indicating an elapsed time from an occurrencetime point of the failure of RRC connection establishment procedure.

A processor according to embodiments executes a process of storing, in amemory, a connection establishment failure log related to a failure ofRRC connection establishment procedure with a network. The processorfurther executes a process of transmitting, to the network, theconnection establishment failure log and elapsed time informationindicating an elapsed time from an occurrence time point of the failureof RRC connection establishment procedure.

A storage medium according to embodiments stores a program that causes auser terminal capable of storing a connection establishment failure logrelated to a failure of RRC connection establishment procedure with anetwork, to execute a process of transmitting, to the network, theconnection establishment failure log and elapsed time informationindicating an elapsed time from an occurrence time point of the failureof RRC connection establishment procedure.

Hereinafter, embodiments of the present invention will be described withreference to the accompanying drawings. Note that in the followingdrawing according to the embodiments, identical or similar symbols areassigned to identical or similar portions.

(1) OVERVIEW OF MOBILE COMMUNICATION SYSTEM

FIG. 1 is a configuration diagram of a mobile communication systemaccording to the present embodiment.

As illustrated in FIG. 1, a mobile communication system according to thepresent embodiment includes a plurality of UEs (User Equipments) 100,E-UTRAN (Evolved-UMTS Terrestrial Radio Access Network) 10, and EPC(Evolved Packet Core) 20. In the present embodiment, the E-UTRAN 10 andthe EPC 20 constitute a network.

The UE 100 is a mobile radio communication device, and performs radiocommunication with a cell (hereinafter, referred to as a serving cell)connected thereto. In the present embodiment, the UE 100 corresponds toa user terminal.

In an idle state corresponding to a waiting state, the UE 100 selectsawaiting cell and waits for an instruction from eNB 200 in the selectedcell. A process of changing the waiting cell in the idle state isreferred to as cell reselection. In addition, the UE 100 performs radiocommunication with the serving cell in a connected state correspondingto a communicating state. A process of changing the serving cell in theconnected state is referred to as a handover.

The E-UTRAN 10 includes a plurality of eNBs (evolved Nodes-B) 200. TheeNB 200 corresponds to a base station. The eNB 200 controls a cell andperforms radio communication with the UE 100 connected to the cell. The“cell” is a term used for indicating a minimum unit of a radiocommunication area and has also a function for performing radiocommunication with the UE 100.

For example, the eNB 200 includes a radio resource management (RRM)function, a routing function of user data, and a measurement controlfunction for mobility control and scheduling.

The EPC 20 includes MMEs (Mobility management Entities)/S-GWs(Serving-Gateways) 300, and OAM (Operation and Maintenance) 400.

The MME is a network node for performing various mobility controls forthe UE 100 and corresponds to a control station. The S-GW is a networknode for performing a transfer control of user data, and corresponds toa mobile switching center.

The eNBs 200 are connected to one another through an X2 interface. Inaddition, the eNB 200 is connected to the MME/S-GW 300 through an S1interface.

The OAM 400 is a server device managed by an operator, and performs themaintenance and monitoring of the E-UTRAN 10. The OAM 400 can alsocontrol the UE 100.

Next, configurations of the UE 100 and the eNB 200 will be described.FIG. 2 is a block diagram of the UE 100.

As illustrated in FIG. 2, the UE 100 includes an antenna 101, a radiotransceiver 110, a user interface 120, a GNSS (Global NavigationSatellite System) receiver 130, a battery 140, a memory 150, and aprocessor 160. Although the configuration of the UE 100 having the GNSSreceiver 130 has been described, the UE 100 not having the GNSS receiver130 is also present. In addition, the memory 150 is integrated with theprocessor 160, and this set (that is, a chipset) may be called aprocessor 160′.

The antenna 101 and the radio transceiver 110 are used to transmit andreceive a radio signal. The antenna 101 includes a plurality of antennaelements. The radio transceiver 110 converts a baseband signal outputfrom the processor 160 into a radio signal to transmit the convertedradio signal through the antenna 101, and converts a radio signalreceived by the antenna 101 into a baseband signal to output theconverted baseband signal to the processor 160.

The user interface 120 is an interface between the UE 100 and a user ofthe UE 100, and includes, for example, a display, a microphone, aspeaker, and various buttons. The user interface 120 receives amanipulation from the user, and outputs a signal indicating a content ofthe manipulation to the processor 160.

In order to acquire location information indicating a geographicallocation of the UE 100, the GNSS receiver 130 receives a GNSS signal,and outputs the received signal to the processor 160.

The battery 140 stores a power to be supplied to each block of the UE100.

The memory 150 stores a program executed by the processor 160 andinformation used for a process by the processor 160. Details of theinformation stored in the memory 150 will be described below.

The processor 160 includes a baseband processor that performs modulationand demodulation, encoding and decoding of the baseband signal, etc.,and a CPU (Central Processing Unit) that executes the program stored inthe memory 150 to perform various processes. The CPU has a function of atimer for counting time. The processor 160 may further include a codecthat performs encoding and decoding of a sound/video signal. Details ofa process performed by the processor 160 will be described below.

The processor 160 acquires location information on the basis of anoutput signal of the GNSS receiver 130. When the UE 100 does not havethe GNSS receiver 130, the processor 160 may execute a positioningmethod (OTDOA method or the like) on the basis of the radio signalreceived by the radio transceiver 110 from the plurality of eNBs 200 (aplurality of cells).

FIG. 3 is a block diagram of the eNB 200. As illustrated in FIG. 3, theeNB 200 includes an antenna 201, a radio transceiver 210, a networkinterface 220, a memory 230, and a processor 240.

The antenna 201 and the radio transceiver 210 are used to transmit andreceive a radio signal. The antenna 201 includes a plurality of antennaelements. The radio transceiver 210 converts a baseband signal outputfrom the processor 240 into a radio signal to transmit the convertedradio signal through the antenna 201, and converts a radio signalreceived by the antenna 201 into a baseband signal to output to theprocessor 240.

The network interface 220 is used for communication performed over theX2 interface and the S1 interface.

The memory 230 stores a program executed by the processor 240 andinformation used for a process by the processor 240.

The processor 240 includes a baseband processor that performs modulationand demodulation, and encoding and decoding of the baseband signal and aCPU that executes the program stored in the memory 230 to performvarious processes. Details of a process performed by the processor 240will be described below.

FIG. 4 is a protocol stack diagram of a radio interface.

As illustrated in FIG. 4, the radio interface protocol is divided intolayers 1 to 3 of an OSI reference model, and the layer 1 is a physical(PHY) layer. The layer 2 includes a MAC (Media Access Control) layer, anRLC (Radio Link Control) layer, and a PDCP (Packet Data ConvergenceProtocol) layer. The layer 3 includes an RRC (Radio Resource Control)layer.

The PHY layer performs encoding and decoding, modulation anddemodulation, antenna mapping and demapping, and resource mapping anddemapping. The PHY layer provides a transmission service to an upperlayer by using a physical channel. Between the PHY layer of the UE 100and the PHY layer of the eNB 200, data is transmitted through thephysical channel.

The MAC layer performs preferential control of data, and aretransmission process and the like by hybrid ARQ (HARQ). Between theMAC layer of the UE 100 and the MAC layer of the eNB 200, data istransmitted through a transport channel. The MAC layer of the eNB 200includes a transport format of an uplink and a downlink (for example, atransport block size, and a modulation and coding scheme) and a MACscheduler for determining a resource block.

The RLC layer transmits data to an RLC layer of a reception side byusing the functions of the MAC layer and the PHY layer. Between the RLClayer of the UE 100 and the RLC layer of the eNB 200, data istransmitted through a logical channel.

The PDCP layer performs header compression and extension, and encryptionand decryption.

The RRC layer is defined only in a control plane. Between the RRC layerof the UE 100 and the RRC layer of the eNB 200, data is transmittedthrough a radio bearer. The RRC layer controls the logical channel, thetransport channel, and the physical channel in response toestablishment, re-establishment, and release of the radio bearer. Whenan RRC connection is established between the RRC of the UE 100 and theRRC of the eNB 200, the UE 100 is in a connected state, and when the RRCconnection is not established, the UE 100 is in an idle state.

A NAS (Non-Access Stratum) layer positioned above the RRC layer performssession management or mobility management.

FIG. 5 is a configuration diagram of a radio frame used in the mobilecommunication system. The mobile communication system employs each ofOFDMA (Orthogonal Frequency Division Multiplexing Access) in a downlinkand SC-FDMA (Single Carrier Frequency Division Multiple Access) in anuplink.

As illustrated in FIG. 5, the radio frame includes 10 subframes arrangedin a time-period direction, wherein each subframe includes two slotsarranged in the time-period direction. Each subframe has a length of 1ms and each slot has a length of 0.5 ms. Each subframe includes aplurality of resource blocks (RBs) in a frequency direction, and aplurality of symbols in the time-period direction. Each symbol isprovided at a head thereof with a guard interval called a cyclic prefix(CP).

In the downlink, an interval of several symbols at the head of eachsubframe is a control region mainly used as a physical downlink controlchannel (PDCCH). Furthermore, the other interval of each subframe is adata region mainly used as a physical downlink shared channel (PDSCH).

In the uplink, both ends in the frequency direction of each subframe arecontrol regions mainly used as a physical uplink control channel(PUCCH). Furthermore, the center part in the frequency direction of eachsubframe is a data region mainly used as a physical uplink sharedchannel (PUSCH).

(2) OVERVIEW OF MDT

The mobile communication system according to the present embodimentsupports Logged MDT which is one kind of MDT. Although details of theLogged MDT are described in Non Patent Literature 1, an overview of theLogged MDT defined in the current specification will be described.

In the Logged MDT, the UE 100 in the idle state performs measurement ofa radio environment (for example, a reference signal received power(RSRP)) and a reference signal received quality (RSRQ) according toconfiguration (Logged Measurement Configuration) instructed from anetwork, and stores the measurement result together with locationinformation and time information as an MDT measurement log.

The configuration of the MDT includes various parameters such as ameasurement trigger, a measurement period, and a network time. Themeasurement trigger is a parameter for designating an event performingmeasurement. The measurement period is a parameter for designating aperiod until an MDT measurement process is finished from theconfiguration of the MDT is set. The network time is a parameter servingas a criterion of the time information.

Upon receiving the configuration of the MDT (the Logged MeasurementConfiguration) from the network in the connected state, the UE 100 setsthe measurement period included in the configuration to a Duration timerwithin the UE 100 and starts the Duration timer. In the idle state, whenthe event designated by the measurement trigger is detected, the UE 100performs measurement of the radio environment, and stores the MDTmeasurement log which includes the measurement result, the locationinformation, and the time information. The location information includedin the MDT measurement log is information lately acquired within a validtime. Furthermore, the time information is generated on the basis of thenetwork time of the measurement parameters. Specifically, the timeinformation includes the network time (a criterion time) included in theconfiguration of the MDT and an elapsed time (a relative time) until themeasurement is performed from the network time. Accordingly, the networkcan estimate a network time at the time of the measurement from thenetwork time (the criterion time) and the elapsed time (the relativetime).

When the MDT measurement log is stored, the UE 100 monitors whether ornot a transmission event of Availability Indicator (notificationinformation) occurs. The transmission event of the AvailabilityIndicator means that the UE 100 establishes or re-establishes connectionwith the network. Specifically, the transmission event of theAvailability Indicator denotes transmission from the idle state to theconnected state (RRC connection establishment), execution of a handover(RRC connection re-establishment), and a new configuration at an RRClayer (RRC re-configuration).

Upon receiving a transmission request of the MDT measurement log fromthe network in response to the Availability Indicator, the UE 100transmits (reports) the stored MDT measurement log to the network. Ifthe eNB 200 or the OAM 400 finds a coverage problem on the basis of theMDT measurement log acquired in this way, the eNB 200 or the OAM 400 canperform network optimization for notifying an operator of the foundcoverage problem or solving the found coverage problem.

When the Duration described above expires, the UE 100 starts a 48-hourtimer that counts time (48 hours in the specification) for retaining thelog. The UE 100 needs to retain the MDT measurement log without deletinguntil the 48-hour timer expires. Here, when the 48-hour timer expireswithout receiving the transmission request of the MDT measurement logfrom the network, the UE 100 may delete the MDT measurement log.

(3) OVERVIEW OF ACCESS PROCEDURE TO NETWORK

FIG. 6 is a sequence diagram of an access procedure (RRC connectionestablishment procedure) when the UE 100 performs the access to thenetwork (the eNB 200). Although details of the access procedure (arandom access procedure) are described in, for example, TS36.321, anoverview thereof will be described below.

The access procedure illustrated in FIG. 6 is started when the UE 100performs an initial connection or a re-connection to the network (theeNB 200). Prior to step S1, the UE 100 establishes the synchronizationwith the eNB 200 in the downlink by a cell search, receives and decodesthe broadcast information (MIB and SIB) from the eNB 200, and starts therandom access process to establish the synchronization in the uplink.

The RRC connection establishment procedure is started by requesting anRRC connection establishment from an RRC layer to a MAC layer in UE 100.The UE 100 starts a timer called as T300 when starting the RRCconnection establishment procedure. The T300 is a timer defining anupper limit time to continue the RRC connection establishment procedure.

As illustrated in FIG. 6, in step S1, the UE 100 transmits a randomaccess preamble to the eNB 200 over a random access channel (RACH). TheRACH is mapped onto a physical random access channel (PRACH).Specifically, the eNB 200 transmits information about resources (randomaccess resources) available for transmission of the random accesspreamble by a broadcast (for example, transmits by SIB2), and the UE 100transmits the random access preamble by using a random access resourceselected from among the available random access resources. The randomaccess resource includes a preamble sequence.

In step S2, after receiving the random access preamble from the UE 100,the eNB 200 performs delay estimation between the UE 100 and the eNB 200on the basis of the random access preamble and determines a resource tobe used in step S3. The eNB 200 transmits a random access response as aresponse for the random access preamble to the UE 100 over the DL-SCH.The random access response includes a timing correction value based on aresult of the delay estimation and the determined assigned resourceinformation.

Here, the UE 100 may not always normally receive the random accessresponse from the eNB 200. When the random access response from the eNB200 is not received within a predetermined time (a time window width)after the transmission of the random access preamble, that is, when therandom access process onto the eNB 200 fails, the UE 100 reselects therandom access resource and starts the random access process (step S1)again. When the random access is started again, a transmission power ofthe random access preamble is increased by a predetermined step size.The transmission of the random access preamble may be performed multipletimes, and even when the transmission of the random access preamble isperformed multiple times, the random access process may not besuccessful.

Further, in step S1, when the plurality of UEs 100 transmit the randomaccess preamble by the same random access resource (the preamblesequence), access contention occurs. In such a case, in step S2, sincethe plurality of UEs 100 respond to the random access responsetransmitted from the eNB 200, a collision occurs. Such access contentionis solved by the RRC connection establishment process.

In step S3, after receiving the random access response from the eNB 200,the UE 100 transmits a connection establishment request (RRC ConnectionRequest) to the eNB 200 over the CCCH by using the resource indicated bythe random access response. The connection establishment requestincludes identification information (a temporary identifier) of the UE100. Furthermore, the UE 100 transmits the connection establishmentrequest and starts a timer called TS300.

In step S4, after receiving the connection establishment request fromthe UE 100, the eNB 200 transmits a connection establishment response asa response for the connection establishment request to the UE 100 overthe CCCH. The connection establishment response is a positive response(RRC Connection Setup) or a negative response (RRC Connection Reject).The connection establishment response includes the identificationinformation of the UE 100 as a transmission destination.

Upon normally receiving the connection establishment response(acknowledge or unacknowledged) from the eNB 200, the UE 100 stops theT300 timer. In addition, the UE 100 checks whether or not the UEidentification information included in the connection establishmentresponse matches the UE identification information transmitted from theUE 100 in step S3. When the UE identification information matches eachother, the UE 100 determines that the connection establishment responseis addressed to the UE 100 and the connection establishment with the eNB200 is completed.

In contrast, when the UE identification information does not match eachother, the UE 100 determines that the connection establishment responseis not addressed to the UE 100. In such a case, the UE 100 determinesthat the RRC connection establishment process fails, reselects therandom access resource, and starts the random access process (step S1)again.

When the connection establishment response from the eNB 200 is notreceived, that is, when the connection establishment response is notreceived before the T300 timer expires, the UE 100 determines that theRRC connection establishment process fails, reselects the random accessresource, and starts the random access process (step S1) again.

Below, the failure of RRC connection establishment procedure mainlyrefers to the expiry of T300 timer without stopping it.

(4) OPERATION ACCORDING TO EMBODIMENT

Hereinafter, the operation of the mobile communication system accordingto the present embodiment will be described while focusing on theoperation of the UE 100.

When the access procedure illustrated in FIG. 6 fails, if the networkrecognizes information about the access failure, by optimizing theparameter of, for example, the eNB 200, it is possible to reduce theoccurrence frequency of the subsequent access failure. However, in thecurrent specification, as a result of the access failure, when the UE100 maintains the idle state, there is a problem in that the informationabout the access failure is not reported to the network.

Accordingly, when the RRC connection establishment procedure (accessprocedure) fails, the UE 100 according to the present embodiment storesa connection establishment failure log (access failure log) related tothe access failure. Even though the configuration (Configuration) fromthe network is not performed, if the access to the network fails, the UE100 stores autonomously the connection establishment failure log. Thisoperation is different from the MDT that does not store the log if theconfiguration from the network is not performed.

Hereinafter, the storing and reporting of the connection establishmentfailure log will be described.

(4.1) Management of Memory Area

When the UE 100 stores both the MDT measurement log and the connectionestablishment failure log, it is necessary to manage the memory area ofthe memory 150 of the UE 100 so that each log can be appropriatelystored. In the present embodiment, the processor 160 of the UE 100reserves a dedicated memory area for storing the connectionestablishment failure log. Further, the processor 160 stores theconnection establishment failure log in the reserved dedicated memoryarea.

FIG. 7 is a diagram for describing a method 1 of managing a memory areaaccording to the present embodiment.

As illustrated in FIG. 7, the processor 160 reserves previously adedicated memory area 150-2 for storing the connection establishmentfailure log in the memory 150 in addition to a memory area (apredetermined memory area) 150-1 for storing the MDT measurement log. Inthe specification, a capacity of the memory area 150-1 for storing theMDT measurement log is defined as at least 64 kilobytes. The processor160 stores the connection establishment failure log in the reserveddedicated memory area.

FIG. 8 is a diagram for describing a method 2 of managing a memory areaaccording to the present embodiment.

As illustrated in FIG. 8, the processor 160 reserves the dedicatedmemory area 150-2 for storing the connection establishment failure logwithin the memory area 150-1 for storing the MDT measurement log. Insuch a case, it is necessary to control the memory area 150-1 so as notto be filled with the MDT measurement log. For this reason, when a dataamount of the MDT measurement log exceeds a threshold value, by notstoring the MDT measurement log subsequent to exceeding the thresholdvalue, the processor 160 reserves the dedicated memory area 150-2.Accordingly, it is possible to previously reserve the dedicated memoryarea 150-2 within the memory area 150-1.

Alternatively, when necessary, the dedicated memory area 150-2 maytemporarily be reserved within the memory area 150-1. Specifically, whenan empty area capable of storing the connection establishment failurelog does not exist within the memory area 150-1, the processor 160reserves the dedicated memory area 150-2 within the memory area 150-1,by deleting a part of the MDT measurement log stored within the memoryarea 150-1.

In this way, the UE 100 capable of storing the MDT measurement logrelated to the radio environment measured on the basis of theinstruction from the network and the connection establishment failurelog related to the access failure to the network, reserves the dedicatedmemory area 150-2 for storing the connection establishment failure log.The UE 100 stores the connection establishment failure log in thereserved dedicated memory area 150-2.

Accordingly, since the connection establishment failure log and the MDTmeasurement log can be separately stored, it is possible to individuallytransmit the MDT measurement log and the connection establishmentfailure log to the network. Thus, the network needs not to perform acomplicate process of distinguishing the MDT measurement log and theconnection establishment failure log to separate them.

In the method 1 of managing a memory area illustrated in FIG. 7, sincethe UE 100 reserves previously the dedicated memory area 150-2 forstoring the connection establishment failure log separated from thememory area 150-1 for storing the MDT measurement log, a consumptionamount of the memory area of the memory 150 increases, but theconnection establishment failure log can be more securely storedseparately from the MDT measurement log.

In the method 2 of managing a memory area illustrated in FIG. 8, sincethe dedicated memory area 150-2 for storing the connection establishmentfailure log is temporarily reserved within the memory area 150-1 forstoring the MDT measurement log, the UE 100 can store the connectionestablishment failure log separately from the MDT measurement log whilesuppressing the consumption amount of the memory area of the memory 150.

(4.2) Content of Connection Establishment Failure Log

Next, the content of the connection establishment failure log accordingto the present embodiment will be described.

The connection establishment failure log according to the presentembodiment includes a cell ID of a cell to which the UE 100 fails toperform RRC connection establishment (access), the number oftransmissions of the random access preambles, the radio environment whenthe UE 100 fails to access (the radio environment related to the cell towhich the UE 100 fails to access), and a reselection reason of therandom access resource. The connection establishment failure log mayfurther include time information and location information. Details ofthe time information in the connection establishment failure log will bedescribed below. In addition, the connection establishment failure logmay include movement speed information acquired on the basis of thelocation information.

The “reselection reason of the random access resource” included in theconnection establishment failure log will be described here. Asdescribed above, the access to the network includes: a random accessprocess onto the network; and a connection establishment process thatestablishes a connection with the network after the random accessprocess. The UE 100 capable of storing the connection establishmentfailure log related to the access failure to the network reselects therandom access resource used for the random access process whenever theaccess failure (failure of the random access process or failure of theconnection establishment process) occurs.

The UE 100 stores the connection establishment failure log inassociation with the reselection of the random access resource.Specifically, when the random access resource is reselected at the timeof the access failure, the UE 100 adds information indicating a reasonof the reselection to the connection establishment failure log for theaccess failure. In addition, one connection establishment failure logcorresponds to the same random access resource and a new connectionestablishment failure log can be generated whenever the random accessresource is reselected.

The random access process includes a process of transmitting the randomaccess preamble to the network from the UE 100 and a process oftransmitting the random access response to the UE 100 from the network.The connection establishment process includes a process of transmittingthe connection establishment request to the network from the UE 100 anda process of transmitting the connection establishment response to theUE 100 from the network.

The reselection reason of the random access resource is that forexample, the UE 100 does not receive the random access response, the UE100 does not receive the connection establishment response, or theidentification information of the UE 100 is not included in theconnection establishment response received by the UE 100.

“The UE 100 does not receive the random access response” means that theUE 100 does not receive the random access response within the timewindow width after transmitting the random access preamble. “The UE 100does not receive the connection establishment response” means that theUE 100 does not receive the connection establishment response before theT300 timer expires after transmitting the connection establishmentrequest. “The identification information of the UE 100 is not includedin the connection establishment response received by the UE 100” meansthat the UE 100 is not selected as a result of the access contention.

The access failure due to the reason that the UE 100 does not receivethe random access response and the access failure due to the reason thatthe UE 100 does not receive the connection establishment response can beimproved by optimizing the parameter of the eNB 200. Meanwhile, theaccess failure due to the access contention is difficult to be improvedeven by optimizing the parameter of the eNB 200. Accordingly, thereselection reason of the random access resource included in theconnection establishment failure log may include only the reason that“the UE 100 does not receive the random access response” and the reasonthat “the UE 100 does not receive the connection establishmentresponse”. Alternatively, the connection establishment failure log forthe access failure due to the access contention may be deleted.

In this way, by storing the connection establishment failure log inassociation with the reselection of the random access resource, it ispossible to effectively store the connection establishment failure loghaving high usefulness.

(4.3) Time Information

Next, the “time information” included in the connection establishmentfailure log will be described.

As described above, in the UE 100 to which the MDT is configured(Configuration), since the network time (criterion time) is included inthe configuration, the elapsed time until the measurement is performedfrom the network time is counted by the timer and the time informationat the time of measuring is obtained.

Meanwhile, since the connection establishment failure log needs to bestored even in the UE 100 to which the MDT is not configured(Configuration), the network time as a criterion may not be present inthe UE 100. In such a case, it is difficult to obtain the timeinformation at the time of the access failure.

Accordingly, in the present embodiment, the time information at the timeof the access failure is obtained as follows. FIG. 9 is a diagram fordescribing the time information according to the present embodiment.

As illustrated in FIG. 9, in step S11, when the access failure occurs,the UE 100 starts the timer (hereinafter, referred to as a “timer forelapsed time”) for counting the elapsed time until the connectionestablishment failure log is transmitted. In the present embodiment, theUE 100 needs to retain the connection establishment failure log withoutdeleting until a value of the timer for elapsed time reaches a thresholdvalue.

In step S12, when the connection establishment failure log is stored andthen the transmission event of the Availability Indicator occurs, the UE100 transmits the Availability Indicator indicating that the connectionestablishment failure log is stored to the network (the eNB 200). Thetransmission event of the Availability Indicator of the connectionestablishment failure log may be the same as the transmission event ofthe Availability Indicator of the MDT measurement log. Further, the UE100 may generate the elapsed time information indicating the elapsedtime until the connection establishment failure log is transmitted fromthe occurrence of the access failure on the basis of the value of thetimer for elapsed time started in step S11.

It is described in the assumption that the eNB 200 requests thetransmission of the connection establishment failure log to the UE 100on the basis of the Availability Indicator.

In step S13, the UE 100 transmits the stored connection establishmentfailure log to the eNB 200 in response to the request from the eNB 200.At this time, the UE 100 transmits the value (the elapsed timeinformation) of the timer for elapsed time started in step S11 whilebeing included in the connection establishment failure log.

In step S14, the eNB 200 receives the connection establishment failurelog and the elapsed time information from the UE 100 and estimates thenetwork time corresponding to the occurrence time point of the accessfailure on the basis of the elapsed time information and the networktime managed by the network. Specifically, the eNB 200 estimates thenetwork time corresponding to the occurrence time point of the accessfailure by subtracting the elapsed time that is indicated by the elapsedtime information, from the network time at the time point of receivingthe connection establishment failure log and the elapsed timeinformation from the UE 100. Here, although it has been described thatthe estimation is performed by eNB 200, the estimation may be performedby the OAM 400.

In this way, even when the network time as a criterion is not present inthe UE 100, the network can estimate the network time corresponding tothe occurrence time point of the access failure.

FIG. 9 illustrates a case where the connection establishment failure logfor the access failure at one time is transmitted to the network.However, when a plurality of connection establishment failure logs foraccess failure occurring multiple times are transmitted all together tothe network, it is necessary to change as follows.

Specifically, after starting the timer for elapsed time, when new accessfailure occurs, the UE 100 stores a value of the timer for elapsed timeat the occurrence time point of the new access failure.

For example, when an connection establishment failure log 1 for firstaccess failure is stored and second access failure occurs, the UE 100stores a value (elapsed time information 1) of the timer for elapsedtime at the time point of the second access failure.

Thereafter, when the connection establishment failure log 1 for thefirst access failure and an connection establishment failure log 2 forthe second access failure are together transmitted to the network, theUE 100 adds the elapsed time information 1 to the connectionestablishment failure log 2 and also adds a value (elapsed timeinformation 2) of the timer at a current time point to the connectionestablishment failure log 1.

Upon receiving the connection establishment failure logs 1 and 2, bysubtracting the elapsed time information 2 from the current networktime, the network estimates the network time (network time 1) at thetime point of the access failure corresponding to the connectionestablishment failure log 1.

In addition, by adding the elapsed time information 1 to the estimatednetwork time 1, the network estimates the network time (network time 2)at the time of the access failure corresponding to the connectionestablishment failure log 2.

In this way, even when the multiple times of access failure until thelog is transmitted occur, the network time at the time of the accessfailure can appropriately be estimated.

(4.4) Method of Reporting Log

Next, the transmission of the connection establishment failure log (thatis, log reporting) to the network will be described.

In the present embodiment, when the UE 100, which is capable of storingthe MDT measurement log and the connection establishment failure log,stores at least one of the MDT measurement log and the connectionestablishment failure log, the UE 100 transmits, by a predeterminedtrigger, the Availability Indicator (notification information)indicating that the log is stored to the network. The AvailabilityIndicator is configured to be capable of identifying the type of the logstored by the UE 100. In other words, when the UE 100 stores theconnection establishment failure log, the Availability Indicator canindicate that the UE 100 stores the connection establishment failurelog.

Furthermore, after the notification information from the UE 100 isreceived, when the network (the eNB 200) transmits, to the UE 100, a LogRequest (request information) for requesting the transmission of the logon the basis of the notification information, the Log Request may beconfigured to be capable of identifying the type of the log thatrequests the transmission.

FIG. 10 is a sequence diagram of a method 1 of reporting a log accordingto the present embodiment. Hereinafter, it is assumed that the UE 100stores at least one of the MDT measurement log and the connectionestablishment failure log.

As illustrated in FIG. 10, in step S111, when the transmission event ofthe Availability Indicator in the MDT occurs, the UE 100 transmits theAvailability Indicator to the eNB 200. The Availability Indicator isconfigured to be capable of identifying the type of the log stored bythe UE 100. For example, the Availability Indicator includes a one-bitflag indicating whether or not the MDT measurement log is present and aone-bit flag indicating whether or not the connection establishmentfailure log is present. Otherwise, the Availability Indicator may bedivided into the Availability Indicator indicating whether or not theMDT measurement log is present and the Availability Indicator indicatingwhether or not the connection establishment failure log is present.

In this way, in this sequence, a trigger (a predetermined trigger)transmitting the Availability Indicator indicating that the connectionestablishment failure log is stored is the same as the transmissionevent of the Availability Indicator in the MDT.

The eNB 200 distinguishes the type of the log (the MDT measurement logand the connection establishment failure log) stored by the UE 100 onthe basis of the Availability Indicator received from the UE 100. TheeNB 200 determines whether or not the transmission of the MDTmeasurement log is requested and whether or not the transmission of theconnection establishment failure log is requested. A criterion of thedetermination may be manually set by the operator and may beautomatically set by the network depending on the parameter to beoptimized.

In step S112, the eNB 200 transmits the Log Request for requesting thetransmission of the log to the UE 100. The Log Request is configured tobe capable of identifying the type of the log that requests thetransmission. For example, the Log Request includes a one-bit flagindicating whether or not the transmission of the MDT measurement log isrequested and a one-bit flag indicating whether or not the transmissionof the connection establishment failure log is requested. Alternatively,the Log Request may be divided into the Log Request indicating whetheror not the transmission of the MDT measurement log is requested and theLog Request indicating whether or not the connection establishmentfailure log is present.

In step S113, the UE 100 transmits the log of which transmission isrequested (the MDT measurement log or the connection establishmentfailure log) to the eNB 200 on the basis of the Log Request receivedfrom the eNB 200.

In this way, according to the method 1 of reporting a log, the network(the eNB 200) can acquire only a necessary log of the MDT measurementlog and the connection establishment failure log.

FIG. 11 is a sequence diagram of a method 2 of reporting a log accordingto the present embodiment. A difference from the method 1 of reporting alog will be described.

As illustrated in FIG. 11, step S121 is the same as that in the method 1of reporting a log and step S122 is different from that in the method 1of reporting a log. Specifically, in step S122, the eNB 200 requests thetransmission of the log to the UE 100 without distinguishing the MDTmeasurement log and the connection establishment failure log. In such acase, in step S123, the UE 100 transmits all the stored logs to the eNB200 without distinguishing the MDT measurement log and the connectionestablishment failure log.

In this way, according to the method 2 of reporting a log, it ispossible to simplify the process as compared to the method 1 ofreporting a log.

FIG. 12 is a sequence diagram of a method 3 of reporting a log accordingto the present embodiment.

As illustrated in FIG. 12, in step S131, the UE 100 transmits theAvailability Indicator indicating that the MDT measurement log is storedto the eNB 200.

In step S132, the eNB 200 transmits the Log Request for requesting thetransmission of the log to the UE 100 on the basis of the AvailabilityIndicator from the UE 100.

In step S133, the UE 100 transmits the MDT measurement log to the eNB200 in response to the Log Request from the eNB 200. At this time, ifthe connection establishment failure log is stored, the UE 100 transmitsthe Availability Indicator indicating that the connection establishmentfailure log is stored together with the MDT measurement log to the eNB200.

In this way, in this sequence, a trigger (a predetermined trigger)transmitting the Availability Indicator indicating that the connectionestablishment failure log is stored means an event that the Log Requestis received by the UE 100 from the network.

In step S134, the eNB 200 transmits the Log Request requesting thetransmission of the connection establishment failure log to the UE 100on the basis of the Availability Indicator from the UE 100.

In step S135, the UE 100 transmits the connection establishment failurelog to the eNB 200 in response to the Log Request from the eNB 200.

In this way, according to the method 3 of reporting a log, it ispossible to report the connection establishment failure log by addingsome steps to the sequence of reporting the MDT measurement log.

(5) OTHER EMBODIMENTS

It should not be understood that the present invention is limited to thedescriptions and drawings constituting a part of this disclosure. Fromthis disclosure, a variety of alternate embodiments, examples, andapplicable techniques will become apparent to one skilled in the art.

In the present embodiment described above, there has been described acase where the memory area is divided into the memory area for the MDTmeasurement log and the memory area for the connection establishmentfailure log and the MDT measurement log and the connection establishmentfailure log are individually transmitted to the network. However, theMDT measurement log and the connection establishment failure log may bestored together, and the MDT measurement log and the connectionestablishment failure log may be transmitted together. FIG. 13 is adiagram for describing a method of reporting a log according to anotherembodiment. Here, it is assumed that the UE 100 stores at least one ofthe MDT measurement log and the connection establishment failure log. Asillustrated in FIG. 13, in step S201, when the transmission event of theAvailability Indicator in the MDT occurs, the UE 100 transmits theAvailability Indicator to the eNB 200. In step S202, the eNB 200transmits the Log Request for requesting the transmission of the log tothe UE 100. In step 5203, the UE 100 transmits the stored log (the MDTmeasurement log or the connection establishment failure log) to the eNB200 on the basis of the Log Request received from the eNB 200.

In addition, in the present embodiment described above, although theconnection establishment failure log including the reselection reason ofthe random access resource is generated whenever the random accessresource is reselected, only when the timing notifying the random accessproblem to the upper layer (that is, from the layer 2 (MAC) to the layer3 (RRC)), that is, the T300 expires, or when the number of thetransmission random access preambles (the number of transmissions of therandom access preambles) exceeds a threshold value (that is,“preambleTransMax” corresponding to the maximum transmittable number ofthe random access preambles), the connection establishment failure logincluding the factor (the reselection reason of the random accessresource) causing the random access problem may be generated. When thenumber of transmissions of the random preambles exceeds the thresholdvalue, information indicating a procedure (for example, ‘Random AccessResponse not received’, ‘Lost in contention resolution’, or ‘T300 isexpired’) at which the number of transmissions of the random accesspreambles reaches the threshold value may be included in the connectionestablishment failure log.

The aforementioned embodiment has been described that the UE 100commonly uses the timer (the timer for elapsed time) for counting theelapsed time until the connection establishment failure log istransmitted from the occurrence time point of the access failure as thetimer for counting the time (the log retention time) for retaining theconnection establishment failure log.

However, a timer (hereinafter, referred to as a “timer for log retentiontime”) for counting the time for retaining the connection establishmentfailure log (the log retention time) may be further provided separatelyfrom the timer for elapsed time. When the timer for log retention timeis further provided, the elapsed time from an occurrence time point ofthe access failure can be counted by the timer for elapsed time and thetime for retaining the connection establishment failure log (the logretention time) can be counted by the timer for log retention time.

For example, when the first access failure occurs, the UE 100 startsboth the timer for elapsed time and the timer for log retention time.When the second access failure occurs, the UE 100 stores the timer value(the elapsed time) indicated by the timer for elapsed time and restarts(resets) the timer for log retention time. By the restarting the timerfor log retention time, it is possible to extend the time (the logretention time) for retaining the connection establishment failure logalong with an occurrence of new access failure.

As the timer for log retention time, the 48-hour timer used in theLogged MDT may be used.

(6) APPENDIX

As described above, “Logging of failed RRC Connection establishmentswill be supported for LTE and UMTS, i.e., a log will be created when theRRC connection establishment procedure fails, without any explicitlyconfiguration.

However there are still some FFS issues i.e., “the MDT log should allowto distinguish whether the RACH procedure was not successful or whetherT300 expired” and “whether we realize this as a logged MDT report or asa separate procedure (like RLF reports)”. Below, the Accessibilitymeasurement will be described while focusing on the logging andreporting.

(Architecture for Accessibility Measurement)

Accessibility measurement log is created when the RRC connectionestablishment procedure fails. It's assumed there are various causes forRRC connection establishment failure. If the failure is due to networkcongestion or moving out of coverage, it would be difficult for the UEto quickly reconnect to the E-UTRA network. Therefore, we think thecurrent Logged MDT report architecture is also feasible forAccessibility measurement and allows enough flexibility for logretrieval.

Proposal 1: A logged MDT report architecture should be reused forAccessibility measurement.

If the Proposal 1 is agreed, the issue of logging and log indicationshould also be discussed. If the UE has an existing Logged MDTconfigured, it is necessary to decide whether the Accessibility logshould be combined with the log from Logged MDT or whether it should bea separate log. Since the Accessibility log is created without explicitconfiguration, it would be too difficult for the network to sort out MDTmeasurements from accessibility info, and there are no clear advantagesfor having a combined log. With one combined log it would be moredifficult for the UE to indicate to the network the contents of the log.To allow for more flexibility at the network, the UE should send aseparate indicator to inform the network of the availability of theAccessibility log.

Currently the UE is allowed to stop the logging autonomously in case thelog volume exceeds the suitable UE memory. If the Accessibility log iscombined with the log from the Logged MDT for idle mode measurements,the Accessibility measurement may also be stopped. However, we don'tthink the accessibility measurement and logging should be stopped justbecause the logged MDT is stopped due to memory resource constraintsince Accessibility measurement log is quite important for mitigatingAccessibility problem. The most feasible solution therefore is to haveseparate logs for the accessibility measurement and Logged MDTmeasurement.

Proposal 2: The accessibility measurement and logging should continueeven if the logged MDT is stopped due to memory resource constraint.

Proposal 3: The Accessibility measurement result should be loggedseparately from the other logs; and the UE should be allowed to send anew indicator, separate from the Logged Availability indicator, whenAccessibility log is available.

The memory size to reserve for storing the Accessibility log should bespecified.

(Logging Unit of the Accessibility Measurement)

Another open issue concerns the need for the Accessibility log todistinguish between RACH procedure failure and T300 expiry. To fullyevaluate the Accessibility problem, the location, time of problemoccurrence and procedural issues, should all be known to the NW/RNC/eNBsince the optimization process may be different depending on the causeof the failure. The cause of the Accessibility failure should be storedwhen the Accessibility failure occurs.

In the current specification, the UE can reselect random access resourcewhen “If no Random Access Response is received within the RA Responsewindow, or if none of all received Random Access Responses contains aRandom Access Preamble identifier corresponding to the transmittedRandom Access Preamble” and “if the Contention Resolution is considerednot successful”. Therefore it's beneficial to the network if the RAfailure attempt is logged for each selected RA Preamble.

Proposal 4: The RA failure attempt should be logged for each selected RAPreamble.

(Contents of Accessibility Measurement Log)

The collection of information already available at the network using thecurrent specification should be excluded from measurements. Logging andreporting of information related to the failed random access attemptsare useful; however, measurements of successful access attempts are notessential and should not be logged and reported.

Cell Identification of RA attempts, number of RACH preambles transmittedand radio measurements (i.e., Cell measurements that are available atthe occurrence of the trigger) are useful for optimization and should belogged by UE. The time of the failed access attempts, mobility stateinformation and the selected preamble group may also be of interest forfurther analysis. Location information is also important but we thinkthe GNSS location information should not be required for accessibilitymeasurement. There may not be enough time to prime the GNSS receiver toobtain a valid location fix since RACH transmission isn't a periodicalevent. If the detailed location information is mandated, the UE may notbe able to perform an access attempt until GNSS location measurement isavailable or the UE may have to leave the GNSS receiver on at all times.Since RAN2 has agreed to allow the use E-Cell ID as one of the validmechanism for Requested Location Information. E-Cell ID could beconsidered as the baseline location measurement mechanism for theAccessibility failure case if location information is critical.

Proposal 5: The Accessibility log should include the Cell Identificationof RA attempts, number of RACH preambles transmitted, radio measurementat the occurrence of RA failures and the reason for new RA Resourceselection (e.g., ‘Random Access Response not received’, ‘Lost incontention resolution’, ‘T300 is expired’).

Proposal 6: E-Cell ID should be the considered as the baseline locationmeasurement mechanism for Accessibility failure case. Valid GNSSlocation information and/or UE speed information reception point mayalso be included in the log. FFS whether the GNSS location informationis valid is judged based on RAR reception point.

(Consideration of Time Related Issues)

Whether time stamp of each problem occurrence should be added to theaccessibility log will be considered. Currently, the UE's time stamp isbased on the availability of absolute time provided at MDTconfiguration. However, this is only feasible if the UE is configuredwith Logged MDT. Accessibility measurement is not explicitly configuredand the UE may not have the absolute time information. This may not be abig issue if the time between the occurrence of the accessibilityproblem and the reporting of the problem is completed is relativelyshort. However, there is no guarantee that the time difference will beshort. Due to the accessibility problem it is actually more likely thatthis time difference will be long. Therefore a new mechanism is needed.One feasible option is to introduce a new timer and stored its timer'svalue in case Accessibility problem occurs.

FIG. 14 is an example of a solution for time stamp without the need forabsolute time. FIG. 15 is an example of a solution for time stampwithout the need for absolute time (Timer expired case). As illustratedin FIG. 14, this example uses a countdown timer with a fixed timervalue. It is also assumed that both the eNB and the UE know the timervalue. This timer can also be reused as a log retention timer. Asillustrated in FIG. 15, at timer expiry, the UE should consider thisAccessibility log as invalid and remove it from memory.

In a case where the other option for the coordination with timeinformation is selected, we should define some other log retentionrequirements i.e., there is no requirement to store non-retrieved databeyond 48 hours, or there is no requirement to store non-retrieved dataafter the 48 hour timer which is counting for the other log retentiontime is expired (if 48 hour timer is already running).

Proposal 7: The need for time stamp and log retention timer for theaccessibility log should be considered.

The entire contents of U.S. provisional application No. 61/645,969(filed on May 11, 2012) are incorporated herein by reference.

INDUSTRIAL APPLICABILITY

As described above, the present invention is useful for mobilecommunication fields.

1-5. (canceled)
 6. A communication control method applied to a mobilecommunication system including a user terminal capable of storing aconnection establishment failure log related to a failure of RRCconnection establishment procedure with a network, the method comprisingthe steps of: when starting the RRC connection establishment procedure,starting a timer defining an upper limit time to continue the RRCconnection establishment procedure, by the user terminal; and storingthe connection establishment failure log in association with an expiryof the timer, by the user terminal.
 7. The communication control methodaccording to claim 6, wherein the RRC connection establishment procedureincludes a random access process onto the network, and in the storingstep, the user terminal stores a number of transmissions of randomaccess preambles in the random access process, in the connectionestablishment failure log.
 8. The communication control method accordingto claim 6, wherein in the storing step, when the user terminal detectsa contention of random access preambles, the user terminal storesinformation indicating a detection of the contention, in the connectionestablishment failure log.
 9. A user terminal capable of storing aconnection establishment failure log related to a failure of RRCconnection establishment procedure with a network, comprising: acontroller that starts a timer defining an upper limit time to continuethe RRC connection establishment procedure when starting the RRCconnection establishment procedure, wherein the controller stores theconnection establishment failure log in association with an expiry ofthe timer.
 10. A processor for executing a process to store a connectionestablishment failure log related to a failure of RRC connectionestablishment procedure with a network, the processor provided in a userterminal, wherein the processor executes: a process of starting a timerdefining an upper limit time to continue the RRC connectionestablishment procedure when starting the RRC connection establishmentprocedure; and a process of storing the connection establishment failurelog in association with an expiry of the timer.
 11. (canceled)
 12. Acommunication control method applied to a mobile communication systemincluding a user terminal capable of storing an MDT measurement logrelated to a radio environment measured based on an instruction from anetwork and a connection establishment failure log related to a failureof RRC connection establishment procedure with the network, the methodcomprising: a step of transmitting notification information indicatingthat a log is stored, from the user terminal to the network, by apredetermined trigger, when at least one of the MDT measurement log andthe connection establishment failure log is stored, wherein thenotification information is configured to be capable of identifying atype of the log stored by the user terminal.
 13. The communicationcontrol method according to claim 12, wherein when the user terminalstores the connection establishment failure log, the notificationinformation indicates that the user terminal stores the connectionestablishment failure log.
 14. The communication control methodaccording to claim 12, further comprising: a step of transmitting, fromthe network to the user terminal, request information for requesting atransmission of the log, based on the notification information afterreceiving the notification information from the user terminal, whereinthe request information is configured to be capable of identifying atype of the log for which the transmission is requested by the network.15. The communication control method according to claim 12, wherein thepredetermined trigger is an event that the user terminal establishes orre-establishes a connection with the network.
 16. A user terminalcapable of storing an MDT measurement log related to a radio environmentmeasured based on an instruction from a network and a connectionestablishment failure log related to a failure of RRC connectionestablishment procedure with the network, wherein the user terminaltransmits notification information indicating that a log is stored, tothe network, by a predetermined trigger, when at least one of the MDTmeasurement log and the connection establishment failure log is stored,wherein the notification information is configured to be capable ofidentifying a type of the log stored by the user terminal.
 17. Aprocessor provided in a user terminal, wherein the processor executes: aprocess of storing, in a memory, an MDT measurement log related to aradio environment measured based on an instruction from a network and aconnection establishment failure log related to a failure of RRCconnection establishment procedure with the network; and a process oftransmitting notification information indicating that a log is stored,to the network, by a predetermined trigger, when at least one of the MDTmeasurement log and the connection establishment failure log is stored,wherein the notification information is configured to be capable ofidentifying a type of the log stored by the memory.
 18. (canceled)
 19. Abase station that establishes a connection with a user terminal capableof storing an MDT measurement log related to a radio environmentmeasured based on an instruction from a network and a connectionestablishment failure log related to a failure of RRC connectionestablishment procedure with the network, wherein the base stationtransmits, to the user terminal, request information for requesting atransmission of a log, based on notification information after receivingthe notification information from the user terminal, wherein the requestinformation is configured to be capable of identifying a type of the logfor which the transmission is requested by the base station.
 20. Acommunication control method applied to a mobile communication systemincluding a user terminal capable of storing a connection establishmentfailure log related to a failure of RRC connection establishmentprocedure with a network, the method comprising: a step of transmitting,from the user terminal to the network, the connection establishmentfailure log including elapsed time information indicating an elapsedtime from an occurrence time point of the failure of RRC connectionestablishment procedure.
 21. The communication control method accordingto claim 20, further comprising: a step of starting a timer when thefailure of RRC connection establishment procedure occurs, by the userterminal, wherein in the transmitting step, the user terminal transmitsinformation indicating a value of the timer at a time point oftransmitting the connection establishment failure log, as the elapsedtime information.
 22. The communication control method according toclaim 21, further comprising: a step of retaining the connectionestablishment failure log without deleting until the value of the timerexceeds a threshold value after starting the timer, by the userterminal.
 23. A user terminal capable of storing a connectionestablishment failure log related to a failure of RRC connectionestablishment procedure with a network, wherein the user terminaltransmits, to the network, the connection establishment failure logincluding elapsed time information indicating an elapsed time from anoccurrence time point of the failure of RRC connection establishmentprocedure.
 24. A processor for executing a process of storing, in amemory, a connection establishment failure log related to a failure ofRRC connection establishment procedure with a network, wherein theprocessor further executes a process of transmitting, to the network,the connection establishment failure log including elapsed timeinformation indicating an elapsed time from an occurrence time point ofthe failure of RRC connection establishment procedure.
 25. (canceled)